1. Field of the Invention
The present invention relates to an automatic developing apparatus for manufacturing lithographic printing plates, in particular to a dipping-type automatic developing apparatus.
2. Description of the Related Art
In general, a lithographic printing plate comprises an oleophilic image area that receives ink during a printing process and a hydrophilic non-image area that receives dampening water, Lithographic printing is a printing process of such that, based on the properties of water and printing ink repellent to each other, the oleophilic image area of a lithographic printing plate is taken as an ink-receiving area and the hydrophilic non-image area thereof as a dampening water-receiving area (ink-non-receiving area) so as to produce a difference in ink adhesiveness in the surface of the lithographic printing plate, whereby ink is adhered to only the image area and then it is transferred onto a printing object such as paper to make a print thereon.
For manufacturing the lithographic printing plate, heretofore widely employed is a lithographic printing plate precursor (PS plate) having an oleophilic photosensitive resin layer (image-recording layer) on a hydrophilic support thereof. In general, the lithographic printing plate precursor is exposed through an original image such as a lith film, then the part to be the image area of the image-recording layer is left remaining  and the other unnecessary image-recording layer is dissolved and removed away with an alkaline developer or an organic solvent to thereby make the hydrophilic support surface exposed out to form a non-image area, and the plate-making process comprises the steps gives the lithographic printing plate.
The conventional plate-making process for lithographic printing plate precursors requires, after the exposure, the step of dissolving and removing the unnecessary image-recording layer with a developer or the like, which, however, is problematic in that a developer falling within a more neutral range and giving little waste is required from the viewpoint of the environment and the safety. In particular, recently, the disposal of wastes to be released through the wet treatment is a big subject of concern in the entire industrial world from the viewpoint of the global environment, and the demand for the solution of above-mentioned problem is now increasing more.
On the other hand, recently, a digital technique of electronically processing image information with computer, accumulating and outputting the data has been widely popularized, and various new image-outputting systems applicable to such a digital technique have become put into practical use. With that, a computer-to-plate technique has been specifically noted, which comprises making a high-convergence radiation such as laser light carry a digitalized image information, and scanning and exposing a lithographic printing plate precursor to the light to thereby directly produce a lithographic printing plate not via a lith film. Accordingly, it is one important technical theme to obtain a lithographic printing plate precursor applicable to the technique.
As mentioned above, it has become much more desired Man before to lower the alkaline degree of developer and to simply the processing process with it from both aspects of the consideration of the global environment and the applicability to small  space and low running-cost operation. However, also as mentioned above, the development process generally comprises three steps of development with an alkaline developer having a pH of at least 10, removal of the alkali agent in a rinsing bath, and treatment with a gum liquid essentially comprising a hydrophilic resin; and an automatic developing machine itself for it also takes a large space, and development wastes, rinsing wastes and gum wastes are produced, therefore still giving some problems in point of the environment and the running cost.
As opposed to this, for example, JP-A 2002-91016 proposes a development method with an alkaline liquid containing a nonionic surfactant having a pH of from 10 to 12.5; however, the photosensitive composition contains an alkali-soluble polymer and is therefore problematic in that the development could not be attained at a pH below the range.
On the other hand, for example, Japanese Patent 2938397 describes a lithographic printing plate precursor having, as disposed on a hydrophilic support thereof, an image-forming layer that comprises hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder. The lithographic printing plate precursor may be processed by imagewise exposing it with an IR laser to thereby thermally merge the hydrophobic thermoplastic polymer particles to form an image, then fitting it onto the cylinder of a printer, and on-machine developing it with dampening water and/or ink. However, the method of image formation through such mere thermal fusion and merging of particles is problematic in that the image intensity (adhesiveness to support) is extremely low and the printing resistance is insufficient, though it exhibits good on-machine developability.
To solve the above problem, proposed is a method of manufacturing a lithographic printing plate, which comprises recording an image on a lithographic  printing plate precursor having, on the support thereof, a heat-sensitive layer containing polymer particles, and then, using an automatic processing machine provided with a rubbing member, rubbing the recording surface of the lithographic printing plate precursor in the presence of a developer, with the rubbing member to thereby remove the image-recording layer in the non-exposed area (see JP-A 2003-316021).
However, the alkali level reduction and the process simplification give a great load to the developing process. For example, even though a photosensitive layer could be readily dissolved and removed with an alkaline developer, but it could not be removed with ease with a low-alkaline developer. Accordingly, the photosensitive layer that could not be dissolved but has remained may inevitably again adhere to the plate, thereby giving refuse on the plate and causing problems of bad appearance and after all printing defects. In addition, as the case may be, the remaining photosensitive layer may soil the inside area of the processing machine and the time and the labor needed for the machine maintenance may be thereby increased.
With the tendency toward the alkali level reduction and the process simplification, the processing machine to be used is being converted from a type of dipping in a developer to a type of spraying with a developer in horizontal conveyance.
However, the horizontal conveyance constitution is problematic in that the liquid often scatters and spreads, and the scattered liquid may dry up to form refuse. Naturally, in the horizontal conveyance constitution, the developer may readily dry up during the non-operation of the machine and the rubbing member (brush) and the roller may dry out and are thereby soiled, and the constitution could not evade the problem of refuse formation owing to the soiling. Accordingly, the planning of the horizontal conveyance constitution is extremely difficult, and its technical hurdle is high. 